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Carbon Sequestration in Deep-Sea Sediments

A team of researchers has concluded that deep-sea sediments could provide a virtually unlimited and permanent reservoir for carbon dioxide. The researchers estimate that seafloor sediments within US territory are vast enough to store the nation’s CO2emissions for thousands of years to come.

In a paper published in the Proceedings of the National Academy of Sciences (PNAS), the authors show that injecting CO2 into deep-sea sediments more than 3,000 meters water depth and a few hundred meters of sediment provides permanent geologic storage even with large geomechanical perturbations such as an earthquake.

The exciting thing about this paper is that we show that CO2 injected beneath the seafloor is sequestered permanently. CO2 injected underground on land is buoyant, and hence has the potential to escape back to the surface.

This is not the case under the deep ocean. Because the ocean floor is so cold, liquid CO2 stored beneath the floor is denser than water and will not rise to surface. Furthermore, the top of the injected CO2 plume will form a hydrate, an ice-like solid that plugs up the pore spaces, self-sealing the injected CO2 plume into the deep sea sediments.

—Charles Harvey, MIT

Injecting carbon dioxide into seafloor sediments rather than squirting it directly into the ocean traps the gas, minimizing damage to marine life while ensuring that the gas will not eventually escape to the atmosphere via the mixing action of ocean currents.

At sufficiently extreme deep-sea temperatures and pressures, carbon dioxide moves beyond its liquid phase to form solid and immobile hydrate crystals, further boosting the system’s stability. The scientists say that thus stored, the gas would be secure enough to withstand even the most severe earthquakes or other geomechanical upheaval.

The scientists note that thin or permeable sediments are inappropriate for carbon dioxide storage, as are areas beneath steep deep-sea slopes, where landslides could free the gas. They add that further assessment of the mechanical feasibility of delivering carbon dioxide to the seafloor, as well as study of possible effects on sea levels, is needed.

Other researchers have proposed storing carbon dioxide in geologic formations such as natural gas fields, but terrestrial reservoirs run a risk of leakage.

In terms of capacity, about 22%, or 1.3 million square kilometers, of the seafloor within the US’ exclusive economic zone is more than 3,000 meters deep. The researchers calculate that the annual US emission of carbon dioxide could be stored in sediments beneath just 80 square kilometers.

Supplying the energy demanded by world economic growth without affecting the Earth’s climate is one of the most pressing technical and economic challenges of our time.

Since fossil fuels—particularly coal—are likely to remain the dominant energy source of the 21st century, stabilizing the concentration of atmospheric carbon dioxide will require permanent storage of enormous quantities of captured carbon dioxide safely away from the atmosphere.

—Daniel Schrag, Harvard

The research was funded by the U.S. Department of Energy, the Merck Fund of the New York Community Trust and the Link Foundation.



tom deplume

Seabed injection requires compressing millions of sfc of CO2 to thousands of psi. How much of the coal's energy will be required for such a plan?


My guess is that major emitters such as coal fired power stations are located close to coal deposits mostly over 100km from the continental shelf. The power penalty to pump scrubbed CO2 over this distance and into deep water must be considerable. Now we need to see a working plant that would be financially viable under a carbon scheme such as the European one.

allen Z

What happens to the sequestered gas during an earthquake, underwater landslide, or other disturbing/destructive events?


I just don't understand, why waste all the effort to put in under the ocean floor.

Why not use the sequestered Co2 to feed Algae ponds that make biofuels?


I can just see the enviro-horror movies spawned from this: "The day the earth burped" and black comedies such as "Give Mother a Pepto".

It sounds like a pretty ridiculous scheme to pump gas into the sea floor.

Bill Young

This sounds like it might actually be a useable large scale sequestration scheme. That is a first.

The numbers I've seen, however, show that, unless you get an economic benefit from the CO2 (like improving oil recovery or such), sequestration is not competitive with nuclear power. As noted by Tom, the energy cost of sequestration is quite high-it clobbers the thermodynamics of a coal plant.


Allen Z - "What happens to the sequestered gas during an earthquake, underwater landslide, or other disturbing/destructive events?"

I guess it comes out with the methane calthrites and does this:

"What unleashed the PETM is unclear. Most evidence points to volcanic eruptions that disgorged gigatonnes of carbon dioxide, or coastal reservoirs of methane gas, sealed by icy soil, that were breached by warmer temperatures or receding seas."


I like this a lot better than the idea of just trying to sink the CO2 deep enough in the ocean to make is too cold to come back up. I have seen one figure that indicated the cost of sequestering the CO2 is about 2-3 cents per KiloWatt Hour. Not chicken feed but still worth it. That would bring "clean" coal to 6-7 cents a kwh. Anyone have a price on Nuke? (you'd have to include waste handling costs to be fare.
For a plant that isn't IGCC already thermodynamic loss due to separation is 8-9%. CO2 separation is 90% of the cost of sequestration (I've already included it in the total sequestering costs)
Apparently North America already has about 3000 km. of CO2 pipeline already in existance.

I'd still like to see more effort put into solar. But if we're going to use coal then we should at least use it as responsibly as possible.

Robert Schwartz

Team Looks at Seafloor as Gas Trap By ANDREW C. REVKIN NYTimes, August 8, 2006

Louis Damorin

A quick one, if CO2 is removed from the atmosphere, this means a lot of O2 is removed too at the same time.

Could this create a problem when the % of oxygen in the atmosphere is lowered ?


In my opinion, the two big problems with schemes like this are:

1 - Sudden release of CO2 reserves could result in a serious disaster. It happened to a natural CO2 sink in Cameroon:

2 - Cost of sequestration will increase cost of fuel, causing the rich to think they can buy their way to green nirvana and pushing the price out of range of the poor.

A better solution is to simply use less fuel and therefore emit less CO2. Fewer resources expended on cleanup, cleaner and safer environment, and lower fuel costs as demand goes down.



re sudden release. The point of this scheme is that if you are deep enough and cold enough the CO2 won't go anywhere because its physical properties when cold.

re price: I don't think it's unreasonable to have an energy source include all of it's real costs. The poor are no excuse for polluting since like everything else ecological damage affects them the hardest first. Negavolts are a great idea, but they only go so far. Lower prices just encourage more consumption.


A better Carbon Sequestration would be to take all the SUV from Detriot and dump them in the ocean.


A quick one, if CO2 is removed from the atmosphere, this means a lot of O2 is removed too at the same time.

It's already gone. The rise in CO2 is almost perfectly matched by a drop in O2. It's just that an increase of 100 ppm when you start with 280 is noticeable, but a drop of 100 ppm when you start with 209000 is not. The only way to release O2 is to reduce the CO2, such as in the E2B exhaust treatment scheme (any green plant will do, actually)

Sudden release of CO2 reserves could result in a serious disaster. It happened to a natural CO2 sink in Cameroon

Lake Nyos is tiny compared to the ocean. Deep ocean waters already hold immense quantities of carbonate. Calcium carbonate (shelly bits) rain down from the surface waters, but below ~4km (the carbonate compensation depth) they dissolve. If the ocean overturned like Nyos we're goners, sequestration or no.

Paul Dietz

For a plant that isn't IGCC already thermodynamic loss due to separation is 8-9%.

There is a new solvent process based on chilled ammonia that promises to reduce the cost of extracting CO2 from coal plant flue gases by a factor of 2 or more over the amine process. It also uses much less energy. EPRI and Alsthom are studying this at a pilot scale.

Calvin Brock

Because it is an e-book, and because it will depend heavily for exposure on social media, I hope I can ask readers to promote it insofar as they feel comfortable doing so. I will also ask for your continued understanding as I post original material less frequently over the coming month. very scary movies

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